1. Field of the Invention
The present invention relates to a machine tool having a spindle for receiving a tool for machining a workpiece, and a mechanism for clamping the workpiece.
2. Related Prior Art
Machine tools of this kind are commonly known from the prior art.
Machine tools of this kind generally have tool changing mechanisms with which tools attached to standardized tool holders can be transferred between a tool receptacle in the spindle and a magazine position. In this manner, with a single workpiece clamping, different machining operations using different tools can be performed in succession on the clamped workpiece before it is replaced with a workpiece yet to be machined.
With machine tools of this kind, a very rapid tool change is desirable so as to minimize the time necessary for the machining occurring in one clamping, so that the machine tool's workpiece throughput is high.
A basic prerequisite for machining a workpiece using a tool clamped in the spindle is of course that the surface to be machined on the workpiece is accessible to the tool. In this connection, problems occur with internally hollow, for example bell-shaped workpieces, whose interior must be machined with a tool that, for reasons relating either to design or to clamping technology, cannot be introduced into the workpiece cavity from above. It is conceivable in the case of a bell-shaped workpiece, for example, that for other reasons related to machining technology it is clamped on the mechanism with the large opening downward, only a small opening being present toward the top, through which a milling cutter cannot penetrate into the workpiece cavity in order to perform the machining required there. To allow this machining in the interior of the workpiece to be accomplished, the workpiece must thus be reclamped, causing valuable machining time to be lost.
As an alternative to such a reclamping of the workpiece, it is also known to use a two-piece tool comprising an adapter tool and machining tool, for example the one that can be obtained from the Bilz company of Esslingen in Germany, under catalog numbers FH111992 and SS111991.
The adapter tool has a relatively thin, long shaft which is attached to the standardized tool holder and has at its free end a kind of bayonet fastener. This adapter tool is then introduced into the workpiece cavity through an opening which faces upward. A large lateral opening must then be provided in the workpiece, through which an operator can introduce the machining tool, i.e. for example the milling cutter, laterally into the workpiece cavity, and there slide it onto the free end of the adapter tool and interlock it by turning it. For this purpose, the machining tool has a retaining bore with pins which coact with the adapter tool in the manner of a bayonet fastener.
The result of this is that the workpiece cavity can be machined with a machining tool that could not have been introduced through the small upper opening, although that opening is large enough to receive the shaft of the adapter tool.
This eliminates the reclamping that would otherwise be necessary; it is now also possible to machine workpiece cavities of workpieces which do not have correspondingly large openings even on their underside, so that even a reclamping would not make it possible to machine the workpiece cavity.
On the other hand, however, it is necessary for the workpiece to have a relatively large lateral opening, which not only must allow the machining tool to be introduced into the workpiece cavity, but additionally must allow enough room for the hand of the operator who must interlock the machining tool with the adapter tool in the workpiece cavity.
Large lateral openings of this kind can cause stability problems in the workpiece, and should therefore be as small as possible. On the other hand, however, these lateral openings should be as large as possible to eliminate any risk of injury to the operator, and moreover so that the difficult task of threading the adapter tool into the machining tool can be performed as easily, quickly, and above all safely as possible.
It is clear that manipulations of this kind with adapter tools and machining tools interfere with the normal machining sequence of an otherwise fully automatic machine tool: they considerably reduce workpiece throughput during the machining of such workpieces, and moreover represent a safety risk to the operator.